The use of dual sideband (DSB) modulation has been shown to be very successful in low-distortion parametric audio systems. In DSB modulation, the signal being processed is simply multiplied by a sinusoid. This results in a fairly wideband signal, with harmonics distributed throughout a wide ultrasound band. In fact, it can be shown that these harmonics extend infinitely across bandwidth, although their levels decrease for frequencies away from the carrier frequency. Therefore, in order to reproduce audible sound with low distortion, one would have to reproduce as much of this spectrum as possible. This requires the use of very broadband transducers and amplifier systems, and the assumption that the transducer and amplifier system has a perfectly flat frequency response (or is corrected by suitable equalization).
However, it is often advantageous to reduce the bandwidth required for the ultrasonic signal. For example, it may be of some advantage to consider a more general form of modulation, which permits greater control over the resulting bandwidth of the modulated signal. While there may be occasional need to expand the bandwidth utilized by a modulated signal, it may be more important in some instances to generate a modulated signal with minimal bandwidth.